This invention relates to a independent metering valve and, more particularly, to an independent metering valve having four independently operable electrohydraulic displacement controlled metering spool valves and method for calibrating the spool valves.
Controlling an operation of a hydraulic output device in a hydraulic circuit is conventionally accomplished using a single spool type valve. The single spool valve has a series of metering slots which control flows of hydraulic fluid in the hydraulic circuit including a flow from a pump to the hydraulic output device and a flow from the hydraulic output device to a tank. When the hydraulic output device is a hydraulic cylinder, these flows are commonly referred to as pump-to-cylinder flow and cylinder-to-tank, respectively.
The metering slots are machined into the stem of the spool valve. With this arrangement, slot timing and modulation are fixed. In order to modify the performance of the hydraulic circuit, the stem must be remachined. Furthermore, in order to add features to the performance of the hydraulic circuit, an entirely new stem may be required. This makes adding features or optimizing the performance of the hydraulic circuit expensive and time consuming.
In one aspect of the present invention, a system for calibrating a independent metering valve is provided. The system includes an actuator having a first and second actuating chamber. The metering valve includes an input port, an output port, and a pair of control ports. A first independently operable electrohydraulic displacement controlled spool valve is disposed between the input port and the control ports and is moveable between a open position and a closed position. A second independently operable electrohydraulic displacement controlled spool valve is disposed between the input port and the control ports and is moveable between a open position and a closed position. A third independently operable electrohydraulic displacement controlled spool valve is disposed between the outlet port and the control ports and is moveable between a open position and a closed position. A fourth independently operable electrohydraulic displacement controlled spool valve is disposed between the outlet port and the control ports. A controller positions three of the spool valves and slowly moves one of the valves from the closed position toward the open position until fluid from the actuating chamber is allowed to flow through the moving valve and the position at which fluid is produced is used for calibrating the valve.
In another aspect of the present invention, a method of calibrating an independent metering valve having a first independently operable electrohydraulic displacement controlled spool valve disposed between an input port connected to a pump and a first control port connected to a head end chamber of a hydraulic actuator, a second independently operable electrohydraulic displacement controlled spool valve disposed between the input port and a second control port connected to a rod end chamber of the hydraulic actuator, and third and fourth independently operable electrohydraulic displacement controlled spool valves disposed between an outlet port and the first and second control ports, respectively, the method comprising the steps; positioning three of the spool valves to one of a closed position and a closed position, moving one of the spool valves from a closed position toward a open position until fluid from the actuating chamber is allowed to flow through the moving valve, and recording the position at which fluid flow is produced through the valve and this position to be used as an offset whenever the valve is used.